This invention generally relates to an electrical ground detection circuit and more particularly, to a capacitively coupled electrical ground detection circuit which determines whether an assembly is electrically grounded and/or attached to an electrically grounded member.
Electrical assemblies or modules, which typically comprise several selectively interconnected electrical/ electronic components which cooperatively provide at least one desired function, are usually required to be connected to electrical ground in order to perform their desired function(s) or objective(s). For example and without limitation, an air-bag assembly must normally be physically and/or xe2x80x9cmechanicallyxe2x80x9d connected and/or coupled to a structural member of the vehicle, such as to the body or the xe2x80x9csheet metalxe2x80x9d of a vehicle. This vehicle structural member provides an electrical ground to the assembly. Hence, the existence or non-existence of this electrical grounded arrangement may be used to determine whether the air-bag assembly is physically connected or attached to the vehicle member. Particularly, the air-bag assembly is required to be electrically xe2x80x9cgroundedxe2x80x9d (e.g., coupled to the electrical ground which is provided by the body or the xe2x80x9csheet metalxe2x80x9d of the vehicle), in order to substantially ensure that the air-bag assembly will be protectably inflated in the event of a vehicle collision. Failure to adequately ensure the continued connection of the air-bag assembly to the vehicle body may cause the air bag to be undesirably inflated as the vehicle is driven or may prevent the air-bag from inflating during a vehicle collision.
While some circuits do exist to determine whether electrical assemblies, such as a vehicle air-bag assembly, are and remain xe2x80x9celectrically groundedxe2x80x9d, these circuits are relatively complex, costly, require relatively large amounts of electrical power, are susceptible to transient noise which causes these circuits to be relatively inaccurate or unreliable, and require a relatively inefficient xe2x80x9canalog to digital signal conversionxe2x80x9d device or assembly which further increases the overall inaccuracy, cost, and complexity of these circuits.
There is therefore a need for a new and improved electrical ground detection and/or determination circuit and/or assembly which overcomes some or all of the previously delineated drawbacks of such prior electrical ground detection and/or determination circuits.
It is a first object of the invention to provide an electrical ground detection and/or determination circuit which overcomes some or all of the previously delineated drawbacks of prior electrical ground detection and/or determination circuits or assemblies.
It is a second object of the invention to provide a method for determining whether an electrical assembly is connected to electrical ground and/or is connected to a certain member of a vehicle.
According to a first aspect of the present invention a circuit is provided for use in combination with an electrical assembly of the type which is to be connected to an electrically grounded member. The circuit includes a voltage source which produces an amount of voltage; a first capacitor; a second capacitor which is coupled to the voltage source; a resistor which is coupled to the first and second capacitors and to the electrically grounded member and which cooperates with the voltage source and with the second capacitor to cause the first capacitor to communicatively receive said amount of voltage and to cause said received voltage to decrease by a certain amount within a period of time; and a controller which is coupled to the first capacitor, which measures the period of time, and which utilizes the measured period of time to determine whether the electrical assembly is connected to the electrically grounded member.
According to a second aspect of the present invention a method is provided to determine whether an electrical assembly is attached to a member. The method includes the steps of providing a capacitor of the type which may be selectively and electrically charged; coupling the capacitor to the member; causing the capacitor to receive a certain amount of voltage; and using the certain amount of voltage to determine whether the electrical assembly is attached to the member.